1. Field of the Invention
The present invention relates to an inkjet print head that is able to eject ink more stable and easy to assemble during manufacture.
2. Related Art
Drop-on-demand inkjet print head disclosed in U.S. Pat. No. 5,402,159 includes a cavity unit and a piezoelectric actuator. The cavity unit is formed with a plurality of nozzles for ejecting ink and a plurality of pressure chambers in one-to-one correspondence with the nozzles. The piezoelectric actuator includes a plurality of piezoelectric ceramic sheets on which drive electrodes are formed and a plurality of piezoelectric ceramic sheets on which common electrodes are formed. The piezoelectric ceramic sheets with the drive electrodes and the piezoelectric ceramic sheets with the common electrodes are stacked one on the other in alternation. Portions of each piezoelectric ceramic sheet sandwiched between the drive electrodes and the common electrode serve as active portions. The piezoelectric actuator is fixed to the cavity unit such that the active portions are in correspondence with the pressure chambers. By selectively activating (deforming) the active portions, ink is ejected from the corresponding nozzles.
The present applicant has proposed in Japanese Patent-Application Publication No. 2002-19102 an inkjet print head having a cavity unit made from an electrically-conducting material and a piezoelectric actuator whose lowest piezoelectric ceramic sheet is fixed to and in contact with the cavity unit. Drive electrodes are disposed on the lowest piezoelectric ceramic sheet, and a common electrode is disposed on a second piezoelectric ceramic sheet from the bottom. That is, the common electrode closest to the cavity unit is disposed above the drive electrodes via the second ceramic sheet. Each piezoelectric ceramic sheet has a thin thickness of 20 μam to 30 μm. With this configuration, a voltage applied to the drive electrode on the lowest piezoelectric sheet is adversely applied to the cavity unit via the thin lowest piezoelectric sheet and also to water-soluble, i.e., conductive ink, contained in pressure chambers formed in the cavity unit. As a result, when a voltage is applied to a drive electrode in order to eject ink from a corresponding pressure chamber, electric current conducts through the piezoelectric ceramic sheet, the cavity unit, and the ink, to a different drive electrode corresponding to an adjacent pressure chamber. This gives rise to the problem of unstable ejection of ink, and ink being ejected from unintended adjacent pressure chamber.